Method and means for testing magnetic properties of toroid cores



Feb. 28, 1961 R. A. Ma MlLLAN METHOD AND MEANS FOR TESTING MAGNETIC PROPERTIES OF TOROID CORES Original Filed Aug. 2, 1956 2 Sheets-Sheet 1 INVENTOR. RAY/Volvo fll/l/KH/LLAN BY z/4 Feb. 28, 1961 R. A. M MILlLAN METHOD AND MEANS FOR TESTING MAGNETIC PROPERTIES OF TOROID CORES Original Filed Aug. 2, 1956 2 Sheets-Sheet 2 INVENTOR.

RAXMMO 6 NA c/f/z zA/v ETHOD AND MEANS FOR TESTING MAGNETIC PROPERTIES OF TOROID CGRES Raymond A. MacMillan, Greenwood, Mass., assignor to the United States of America as represented by the Secretary of the Air Force @riginal application Aug. 2, 1956, Ser. No. 601,851. Divided and this application Sept. 12, 1957, Ser. No.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to the testing of magnetic materials, and particularly to methods and means for testing toroidal-shaped samples of such magnetic materials.

In order to take measurements of magnetic materials, such material is often formed in the shape of a ring or toroid. These ring samples are then wound with a layer of insulating tape and two or more windings of wire are put over the tape. When many different material compositions are formed into rings of uniform size, each must have electrical windings applied and removed for evaluation and tests. This process is tedious and timeeonsuming even if accomplished with the aid of a toroid winding machine. Furthermore, a toroid winding machine does not always accommodate the large dilference m wire diameter that would be convenient to use for magnetlc measurements.

Objects of the invention are to provide methods and structures to expedite the determination of the magnetic chadracteristics of test samples of materials to be evaluate More specifically, objects of the invention are to provide methods and structures facilitating application of a preformed current conductor to each of a series of test samples in succession, in a manner to permit rapid transfer from one to another of the series.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings, wherein:

Fig. 1 shows separately the toroidal sample and concentric insulators;

Fig. 2 shows the first stage of assembly with partial application of the detector Winding;

Fig. 3 shows a plan view in cross section of the sample after application of the detector winding and insulators;

Pig. 4 shows the second stage of assembly with partial application of the primary winding;

Fig. 5 is the thumb screw clamping bar used in mounting the coils; and

Fig. 6 shows the device completely mounted and in operative form.

As will be clear from the drawings, the magnetic core sample 1 is surrounded by two insulator rings 2 and 3 which fit the inside and outside peripheries of the core sample 1 snugly. The insulator rings 2 and 3 may be made of Teflon about 0.05" thick which was chosen in laboratory tests as the material for the insulating rings to support the winding springs 4 and 7 because of its low coefficient of friction together with its mechanical strength and its excellent electrical characteristics. The anti-friction characteristic of this material allows easy threading of close fitting windings of fine wire and many turns. An alternative method would be the use of Tefloncovered spring wire which would have the advantage of ice permitting the turns to be in contact allowing more turns to be used and eliminating the first two insulating rings 2 and 3.

The windings are made of a substance such as preformed Phosphor bronze springs which are threaded over the Teflon insulators inclosing the core samples. In laboratory tests the secondary or detector winding 4 Was a 50 turn winding made of 0.020 spring wire wound on a rod with 54 turns to the inch. The primary winding 7 was made of 0.050" spring wire on a /2" rod with a spacing equal to the diameter of the wire. These spring windings 4 and 7 have low electrical resistance, are non-magnetic and withstand large distortions with no permanent change in shape. They can be threaded on and oil the core samples many times without loss of shape. The spring diameter can be determined by trial based on the material used. Too small a diameter makes threading difficult and causes permanent distortion in the spring; too large a diameter makes a bulky assembly and decreases the spacing of the winding from the core sample. This excess spacing is not desirable, particularly in the winding which supplies the measuring instrument because of the possibility of error due to stray fields. This consideration is not so important for the outer winding to which power is supplied.

In this type assembly, shorted turns are a possibility. However, such a condition is easily detected by holding the coil assembly in front of a strong light Where the position of each turn may be readily observed. Correcting such a fault may be simply accomplished by moving the entire coil or the offending turn slightly on the Teflon support rings and allowing the spring winding to assume its natural shape. After the application of the insulators 2, 3, 5 and 6 and the windings 4 and 7, the assembly is mounted on the Bakelite base 8 and held in place by a thumb screw and plastic clamping bar 9. Connections are then made to tapered pins 10 extending through the base mounting. The ends of the inner coil 4 may be formed into two turn loops of small diameter to hold tightly when pushed over the connected tapered pins 10. The heavy outer coil 7 can be formed in like manner. However, there is generally sufficient spring tension stored in the outer coil winding 7 to make a firm contact by means of hooks shaped on the winding ends. The entire assembly can be accomplished without tools in less than four minutes.

Although the invention has been described with reference to particular embodiments it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claim.

This application is a division of co-pending application No. 601,851, entitled Method and Means for Testing Magnetic Properties of Toroid Cores, filed August 2, 1956 by Raymond A. MacMillan.

I claim:

A magnetic structure including in combination, a rigid, one-piece annular core of magnetic material, and an electrical conductor having a helical contour to facilitate its rapid application to, and removal from, said one-piece core by successive threading and unthreading operations.

References Cited in the file of this patent UNITED STATES PATENTS 359,205 Curtis et a1. Mar. 8, 1887 1,570,948 Crouch Jan. 26, 1926 1,695,679 Berlowitz Dec. 18, 1928 1,994,534 Robinson Mar. 19, 1935 2,569,468 Gaugler Oct. 2, 1951 2,674,031 Buhrcndorf Apr. 6, .1954 

